diff --git a/src/vs/workbench/contrib/webview/browser/baseWebviewElement.ts b/src/vs/workbench/contrib/webview/browser/baseWebviewElement.ts
index 05c9310208f..7f97d5592bd 100644
--- a/src/vs/workbench/contrib/webview/browser/baseWebviewElement.ts
+++ b/src/vs/workbench/contrib/webview/browser/baseWebviewElement.ts
@@ -543,6 +543,7 @@ export abstract class BaseWebview<T extends HTMLElement> extends Disposable {
 							mime: result.mimeType,
 							data: buffer,
 							etag: result.etag,
+							mtime: result.mtime
 						});
 					}
 				case WebviewResourceResponse.Type.NotModified:
@@ -552,6 +553,7 @@ export abstract class BaseWebview<T extends HTMLElement> extends Disposable {
 							status: 304, // not modified
 							path: uri.path,
 							mime: result.mimeType,
+							mtime: result.mtime
 						});
 					}
 				case WebviewResourceResponse.Type.AccessDenied:
diff --git a/src/vs/workbench/contrib/webview/browser/pre/service-worker.js b/src/vs/workbench/contrib/webview/browser/pre/service-worker.js
index 9463b4a7764..dfa0a5e08f7 100644
--- a/src/vs/workbench/contrib/webview/browser/pre/service-worker.js
+++ b/src/vs/workbench/contrib/webview/browser/pre/service-worker.js
@@ -100,7 +100,9 @@ class RequestStore {
 
 /**
  * Map of requested paths to responses.
- * @typedef {{ type: 'response', body: any, mime: string, etag: string | undefined, } | { type: 'not-modified', mime: string } | undefined} ResourceResponse
+ * @typedef {{ type: 'response', body: Uint8Array, mime: string, etag: string | undefined, mtime: number | undefined } |
+ *           { type: 'not-modified', mime: string, mtime: number | undefined } |
+ *           undefined} ResourceResponse
  * @type {RequestStore<ResourceResponse>}
  */
 const resourceRequestStore = new RequestStore();
@@ -142,12 +144,12 @@ sw.addEventListener('message', async (event) => {
 				switch (data.status) {
 					case 200:
 						{
-							response = { type: 'response', body: data.data, mime: data.mime, etag: data.etag };
+							response = { type: 'response', body: data.data, mime: data.mime, etag: data.etag, mtime: data.mtime };
 							break;
 						}
 					case 304:
 						{
-							response = { type: 'not-modified', mime: data.mime };
+							response = { type: 'not-modified', mime: data.mime, mtime: data.mtime };
 							break;
 						}
 				}
@@ -233,15 +235,19 @@ async function processResourceRequest(event, requestUrl) {
 			}
 		}
 
-		/** @type {Record<String, string>} */
+		/** @type {Record<string, string>} */
 		const headers = {
 			'Content-Type': entry.mime,
+			'Content-Length': entry.body.byteLength.toString(),
 			'Access-Control-Allow-Origin': '*',
 		};
 		if (entry.etag) {
 			headers['ETag'] = entry.etag;
 			headers['Cache-Control'] = 'no-cache';
 		}
+		if (entry.mtime) {
+			headers['Last-Modified'] = new Date(entry.mtime).toUTCString();
+		}
 		const response = new Response(entry.body, {
 			status: 200,
 			headers
diff --git a/src/vs/workbench/contrib/webview/browser/resourceLoading.ts b/src/vs/workbench/contrib/webview/browser/resourceLoading.ts
index 5b6ebc58ac2..bba1ae1d6b6 100644
--- a/src/vs/workbench/contrib/webview/browser/resourceLoading.ts
+++ b/src/vs/workbench/contrib/webview/browser/resourceLoading.ts
@@ -22,6 +22,7 @@ export namespace WebviewResourceResponse {
 		constructor(
 			public readonly stream: VSBufferReadableStream,
 			public readonly etag: string | undefined,
+			public readonly mtime: number | undefined,
 			public readonly mimeType: string,
 		) { }
 	}
@@ -34,6 +35,7 @@ export namespace WebviewResourceResponse {
 
 		constructor(
 			public readonly mimeType: string,
+			public readonly mtime: number | undefined,
 		) { }
 	}
 
@@ -50,7 +52,7 @@ export async function loadLocalResource(
 	logService: ILogService,
 	token: CancellationToken,
 ): Promise<WebviewResourceResponse.StreamResponse> {
-	logService.debug(`loadLocalResource - being. requestUri=${requestUri}`);
+	logService.debug(`loadLocalResource - begin. requestUri=${requestUri}`);
 
 	const resourceToLoad = getResourceToLoad(requestUri, options.roots);
 
@@ -64,14 +66,14 @@ export async function loadLocalResource(
 
 	try {
 		const result = await fileService.readFileStream(resourceToLoad, { etag: options.ifNoneMatch });
-		return new WebviewResourceResponse.StreamSuccess(result.value, result.etag, mime);
+		return new WebviewResourceResponse.StreamSuccess(result.value, result.etag, result.mtime, mime);
 	} catch (err) {
 		if (err instanceof FileOperationError) {
 			const result = err.fileOperationResult;
 
 			// NotModified status is expected and can be handled gracefully
 			if (result === FileOperationResult.FILE_NOT_MODIFIED_SINCE) {
-				return new WebviewResourceResponse.NotModified(mime);
+				return new WebviewResourceResponse.NotModified(mime, err.options?.mtime);
 			}
 		}